Method of decreasing radius of curvature in return bend



A. HUET Nov. 29, 1955 METHOD OF DECREASING RADIUS OF CURVATURE IN RETURN BEND 3 Sheets-Sheet 1 Filed NOV. 10, 1955 lliliillf A. HUET 2,724,891

METHOD OF DECREASING RADIUS OF CURVATURE IN RETURN BEND Nov. 29, 1955 5 Sheets-Sheet 2 Filed Nov. 10, 1953 fi/VDRE //(/E7' IN V EN TOR. 2

A. HUET 3 Sheets-Sheet 5 Nov. 29, 1955 METHOD OF DECREASING RADIUS OF CURVATURE IN RETURN BEND Filed NOV. 10, 195

United States Patent METHOD OF DECREASING RADIUS OF CURVATURE IN RETURN BEND Andre Huet, Paris, France, assignor to Combustion Engineering, Inc., New York, N. Y., a corporation of Delaware Continuation of abandoned application Serial N 0. 103,271, July 6, 1949. This application November 10, 1953, Serial No. 391,366

3 Claims. (Cl. 29157.6)

The present invention relates to improvements in methods for bending pipes or tubes to form return bends of small radius.

In an application filed on May 13, 1949, under Serial No. 92,994, now Patent No. 2,689,596, issued September 21, 1954, for Process and Apparatus for Bending Tubes to Small Radii, applicant has described a process for production of an elbow, or bend, whose radius of internal curvature is very small in relation to the diameter of the pipe, the particularity of the process residing in the difference in the temperatures to which the external region of the elbow and the internal or crotch region of the elbow are brought before or during the bending operation.

The region situated in the vicinity of the external generatrix of the elbow is maintained at a temperature below that of the region situated about the internal generatrix, or crotch, either owing to a more pronounced heating of the crotch or, on the contrary, by cooling possibly while carrying out the bending, of the external region of the elbow. The result is that the bending, instead of occurring about the center axis of the elbow or bend as in previously known processes, occurs about or in the vicinity of the outermost generatrix of the elbow, so that the radius of curvature of the final bend can be reduced much more than heretofore.

The present invention has for its object an improvement of this process owing to which it is possible to reduce still further the radius of internal curvature of the elbow, and even to obtain elbows whose branches come practically into contact with each other along their length.

To this end, according to the invention, an elbow of already reduced radius of curvature, obtained as just mentioned, is subjected to a heating that afiects a limited zone, situated in the crotch as well as in the external region of the elbow, whereupon the two parallel leg portions of the elbow which in general have remained cold are subjected to an approaching operation moving their axes closer together which upsets the softened metal on itself, producing an increase in the thickness of the walls in these central regions of the elbow, without diminution of the section of internal passage of said elbow.

The heating zone just mentioned and the amount of heating are determined by (1) the thickness of the walls of the elbow, (2) the relative spacing to which it is desired to adjust the two leg portions of the elbow, and (3) the extent of the upsetting stresses, that is, the distance separating the axis of symmetry of the elbow from the point of application of the upsetting stress. It is understood that this distance through which the compressive force is applied is always relatively large in relation to the lateral dimension of the areas in which the metal will be upset, and for this reason the present process is applied not to an elbow of large radius of internal curvature but to an elbow already of relatively small radius, obtained as in the aforementioned patent application.

During the heating operation, the lateral portions of the elbow which must remain cold, or at a lower temperature, may be protected against the action of the heating by screens, or masks, which limit the heat zone defined above. The elbow is then put in an apparatus in which the cold regions of the elbow are held in two jaws, or two semi-matrices, which are brought progressively closer to exert two exactly opposite pressures on the central heated part, so that there is produced an upsetting of the metal in the heated region, while the two leg portions or rectilinear pipes which issue from the elbow are brought closer together.

The same result may be obtained also, without upsetting apparatus, by hammering or swaging with small quick blows in order to bring together the two leg portions or rectilinear pipes of the bend, these having remained cold.

Finally, there is obtained an elbow whose walls are progressively reinforced in proportion to the upsetting caused in the softened region and whose legs may be practically contiguous, while the walls of the said elbow are reinforced, that is, have an extra thickness both in the crotch and in the external region of the elbow, without there being a reduction of the internal section of passage in the elbow.

According to a further improvement of the process, it is possible to bring to a temperature higher than the rest of the elbow those regions of the elbow situated on either side of a central region which is left at a lower temperature, in such a way that when the two branches of the elbow are subjected to two opposite pressures in order to be brought together, the compression of the bend is effected between each cold branch and the me dian central zone which is itself relatively cold, so that there is produced a kind of bending of the branches of the elbow finally to produce an elbow of very small internal radius.

The process and the devices constituting the subject of the invention may be applied to pipes of any section, for example to pipes of oval section, or to pipes whose contour is more or less complicated and presents hollow ribs, whether tangential or not.

The following description referring to the annexed drawings is given by way of example to explain the manner in which the invention may be carried into eifect.

Figure 1 shows in diagrammatic form a bend of already reduced radius of curvature, on which a zone H to be subjected to heating is indicated.

Figure 2 shows the elbow surmounted by shields which insure the delimitation of the heating zone.

Figure 3 shows the elbow of a reduced radius of curvature andheated, disposed in the dies which cause the upsetting of the two sides of the elbow which have remained cold.

Figure 4 is analogous to Fig. 3 after bringing the dies together.

Figure 5 is an end view of Fig. 3.

Figure 6 shows in section the elbow of practically zero radius of internal curvature obtained according to the present invention.

Figures 7 and 8 are similar to Figs. 3 and 4 but illustrate a variant of the two dies.

Figures 9 and 10 show in section bends of pipes of circular section obtained by means of the matrices of Fig. 7. a

Figure 11 represents an elbow disposed in the matrices with indication by hatching of particular heating zone E on the elbow.

Figure 12 is a section of'Figure 11 along a perpendicular plane 1212.

Figure 13 is analogous to Fig. 11 after bringing together the matrices, showing the return bend with its final radius 7 of curvature.

Figures 14 to 17 show tubing whose flattened circular section is extended through two hollow tangential ribs, Figures 14 and 15 representing the bending as carried out in a plane approximately parallel to that of the ribs while in Figures 16 and 17 the bending is in a plane perpendicular to that containing the pipe axes.

' Figures 18 to 21 relate to the bending of a pipe of oval section; Figs. 18 and 19 concern more especially the bending in the plane where the pipe is ovalized; and Figs. 20 and 21, the bending in the perpendicular plane.

As will be seen in Figure 1, an elbow C of already reduced internal radius, that is, a radius less than about one and a quarter times the external diameter of the pipe, obtained for example according to the process described in the aforementioned patent application, is subjected to heating in a region delimited by the rectangle H shown in broken lines, owing to which the crotch K and the external region M of the elbow are softened. It may be well to heat the crotch K over a greater length than the external region M of the elbow, or vice versa.

To protect against the action of the heat, the lateral parts P of the elbow which must remain cold may be disposed, as will be seen in Fig. 2, in shields 20, 21 of suitable form spaced to leave free the region H of the, elbow C which must be heated.

When the desired temperature is reached, the elbow is then put in an apparatus of the type of that which was described in the aforementioned patent application, consist-ing of two plates 22 and 23 (Fig. maintained at a distance corresponding to the external diameter of the pipe a, and having two jaws or semi-matrices 24, 25 which can be brought together by a movement of translation in the direction of the arrows B so as to exert two exactly opposite pressures on the central part of the elbow. There is then produced an upsetting of the metal in the heated region H, this upsetting producing on the one hand an extra thickness of the wall of the pipes, both for the internal wall or crotch K and for the external wall M of the elbow, and insuring at the same time a swelling (instead of a flattening) of the pipe, that is, an increase in, the internal section of the elbow. In fact,.the heating and the pressure exertedareregulated, as a function of the extent over which the, pressure is exerted, in such a way that the upsetting. of the metal occurs toward the exterior or outside of the pipes withrespect; both to the external region M and the crotch region-K. Finally, as willbe; seen inthe sectiontof Fig. 6, there is obtained a 180 bend whose outlet branches- Q- are. almost in contact, thatis, a bend whoseradiusof curvature. ispractically non-existent and whose Walls, both inthe. crotch K and on the end in the, external region M, have. extra thicknesses S.

The process may be applied to pipes ofspecial'. steel.

To insure the swelling, or widening, of. the section of internal passageof the pipe in the elbow it maybe well, in the course of the operation, to cool the external:surface of the elbow in such a way that the; upsetting of the metal occurs always toward the. exterior.

Instead of disposing the elbow in an upsetting apparatus having semi-matrices, it maybe. sufficientato hammer with little blows the lupperparts. ofthetwolegs Q of the bend which have remainedcold.

As will be seen in Figure 7, the working. faces 26,- 27 of the matrices 24, 25Ibetween which the .bend is pressed, need not, at the beginning of the. operation, .applyragainst the entire external region of the elbow but may leave an interval or cavity at the upperpart, which interval allows the metal of this external region, during the operation of compression, to be pushed back outwardly so as not to diminish the internalsection of the passage inside the elbow.

When these work faces26, 27 are-initially spaced still farther from the bend, the final bend is of ogival contour, such as that shown in Figure 10.

During this operationthere is caused an upsetting on itself of the metal of the bend in the crotch region' K softened by the heating, and the legs Q may become practically in contact, as is seen in Figures 9 and 10. In the course of the operation, the walls of the elbow are reinforced, as is seen in Figures 9 and 10, that is, they take on an extra thickness both in the crotch at K and in the external zone, at M, this occurring without the internal section of passage of the elbow being substantially diminished. The bend may be of a rounded form (Fig. 9) or an ogival form (Fig. 10) according to the form of the workv faces of the matrices 24, 25. It will be noted that the extra thickness of the crotch K extends along the legs of the elbow to R, the eiiect being that most satisfactory solidity and strength of the elbow is insured.

The heating of the region H and the pressure of the punches or matrices 24, 25' can be regulated so as to obtain either a simple piling up of metal in the regions K and M or a slidingof the metal from the region K toward the legs as far as shown in the figures, this occurring without there being any excessive extra thickness of the walls, or finally there may be a combination of these two effects of piling up and of sliding.

As will be seen in Fig. 11 the central region of the elbow delimited for example by the rectangle A B C D remains cold or at a less elevated temperature than the shaded regions E which are brought to a higher temperature by any suitable means, for example by heating with a torch. In other words the shoulder portions E of the arched crotch region are heated while the central area A B C D of the crotch that lies between these shoulder portions which merge into the tube legs 12 remains unheated or at least relatively cooler. This being so, when the dies 34, 35 are brought together in the direction of the arrows F, eitherby displacing one of the jaws or preferably by displacing both jaws in opposite directions, there r is obtained an approach of the legs Q of the bend D which then hasthe form indicated in Fig. 13 with a very much reduced radius of internal curvature. During this reduction of the spacing of the tube legs 12' the bend issubstantially fully confined; by the matrices 34, 35 and by the plates which apply restraining forces in two planes that lie parallel to the plane which includes the longitudinal axes of the tube legs 12. Each leg Q of the bend has remained cold and is in some degree compressed against the cold part A B C D, constituting an anvil, and the bend yields and takes on the final form of Fig. 13, this flexure being facilitated by the heating of the shoulder regions E when the metal is-compressed and upset so as to increase the wall thickness of the final bend in these regions.

The heating zone which is outlined in Fig. 11 is given only by way of example. Thus, it would be suflicient to provide a cold zone of approximately triangular form such as is delimited by the contour C I D and to heat, on either side of this zone, the approximately polygonal contours A I D G on the one hand and I B H C on the otherhand, so as to obtain an increase of temperature both in the internal region of the elbow and in the external region of the elbow to facilitate the pressing operation which leads to a bend of very reduced radius of curvature.

One of the advantages of the process just described resides in that the matrices or jaws 34', 35'no longer need to present arched or ogival working faces corresponding to that of the final bend which it is desired to obtain, but may be rectilinear, as is seen in the Figures 1 1, 13 designed simply to press against the straight legs Q of the elbow.

The processof production may be applied to elbows of any section and is not necessarily-limited to elbows of circular section. In Figures 15 to 17 there is shown the elbow obtained in the case of a pipe whose section has the form shown'wherein the pipe k extends along two hollow tangential ribs m1, m2. In Figures 14 and 15 the curving is obtained in a plane approximately parallel to that of'the ribs m1, m2. The curving may takeplace also in a perpendicular planeas is seen in the case of the elbow l of the same pipe section, shown in Figures 16 and 17.

Figures 18 to 21 represent an elbow from pipe of oval section n. In the case of the elbow shown in Figure 18, the bending is obtained in a plane parallel to the plane to the major axis of the pipe. In the case of the elbow 0, shown in Figs. 20 and 21 which is obtained from a pipe of the same section, the bending takes place in a perpendicular plane.

This application is a continuation in part of Serial No. 92,995, filed in my name on May 13, 1949, now abandoned, and a continuation of Serial No. 103,271, filed July 6, 1949, now abandoned.

What I claim is:

1. The method of treating a work piece consisting of a hollow tube bend of malleable metal having parallel tube legs spaced apart a distance greater than the tube radius and joined by an integral 180 elbow which comprises; heating the arched internal crotch region of the hollow bend solely in the shoulder portions thereof that are contiguous to and merge with the tube legs to a temperature rendering the bend malleable while maintaining the exterior region of the elbow opposite said shoulders together with the central portion of the internal crotch region located between said shoulder portions at a lower temperature; and, without supporting or restraining said crotch region of the bend, subjecting the leg portions of the bend to oppositely directed pressures so as to reduce the spacing of said leg portions and bring the tube legs closer together while producing an upsetting of the metal in said shoulder portions which assures an extra thickness of the walls at the locations of said shoulder portions in the final bend.

2. The method of treating a work piece consisting of a hollow tube bend of malleable metal having parallel tube legs spaced apart and joined by an integral 180 elbow which comprises; heating only the shoulder portions of the arched crotch region of the hollow return bend which merge with the leg portions and lie between the latter and a mid-portion of the crotch centered on an axis paralleling the longitudinal axes of the tube legs while maintaining the outer elbow region and said central region of the crotch at a lower temperature; and applying against said tube legs forces acting in opposite directions in a plane including the longitudinal axes of both said legs for moving the tubular legs that extend from the arched bend into side by side, substantially contacting, relation while compressing the said shoulder portions of the crotch region without supporting or restraining said crotch region of the bend.

3. The method of treating a work piece consisting of a hollow tube bend of malleable metal having parallel tube legs spaced apart a distance greater than the tube radius and joined by an integral elbow which comprises; heating the arched internal crotch region of the hollow bend solely in the shoulder portions thereof that are contiguous to and merge with the tube legs to a temperature rendering the bend malleable while maintaining the exterior region of the elbow opposite said shoulders together with the central portion of the internal crotch region located between said shoulder portions at a lower temperature; and, without supporting or restraining said crotch region of the bend, subjecting the leg portions of the bend to oppositely directed pressures so as to reduce the spacing of said leg portions and bring the tube legs closer together while producing an upsetting of the metal in said shoulder portions which assures an extra thickness of the walls at the locations of said shoulder portions in the final bend, and, while said force is applied, maintaining the bend stifily between restraining members applied at both sides of the bend in planes parallel to the plane including both tube axes.

References Cited in the file of this patent UNITED STATES PATENTS 953,253 Brinkman Mar. 29, 1910 1,572,975 Van Meter Feb. 16, 1926 2,278,254 Enghauser Mar. 31, 1942 2,428,825 Arnoldy Oct. 14, 1947 2,433,055 Linden Dec. 23, 1947 2,461,323 Hille Feb. 8, 1949 2,480,774 Rossheim Aug. 30, 1949 2,571,416 Brown Oct. 16, 1951 FOREIGN PATENTS 106,280 Great Britain of 1917 

